The objective is to ascertain if defective tRNA accumulates during aging and causes errors in protein synthesis. The tRNA populations in livers of aging rats will be purified. Their amino acid accepting ability is lower in old animals. We will examine whether in vitro modification improves this functional capacity of old tRNA. We will test the effects of polyamines and other cations on the acylation capacities of young and old tRNAs. We will see if defective tRNA is preferentially bound to ribosomes in old animals, and if the tRNA in living cells is as completely acylated in old animals as it is in young animals. We will examine the completeness of the -CCA ends of tRNAs from animals of different ages. Soluble RNA which is degraded quickly in old animals will be characterized. Phenylalanine tRNA will be prepared and characterized. Glucose-6-phosphate dehydrogenase, which changes in specific activity and isozyme ratio during aging, will be purified. It will be examined using O'Farrell's technique of 2-dimensional isoelectric focusing and SDS gel electrophoresis. If few, definite charge changes have occurred, peptide maps will be prepared and sequence analysis done. If broad, diffuse changes have occurred, fibrinopeptides sequences will be examined instead. In either case, the induction of glucose-6-phosphate dehydrogenase and its turnover will be characterized in young and old animals. In vitro systems for G6PD and possibly fibrinopeptide synthesis will be developed, made tRNA dependent, and used to test the function of young and old tRNAs.